I really want to like Flutter, but I someone really don't want to spend the time to learn Dart. I can't really quantify it--some mix of yet-another Proprietary Google Technology, yet another ecosystem, yet another X. I'm tired I just want to build stuff that solves problems.
Context: I was a Qt developer in a past life.
The alternatives for cross-platform GUI are
1. Electron
2. Frameworks like C++/Qt C/Gtk
3. Bindings to (2)
Using frameworks like Qt in native C++ sucks because C and C++ are just terrible languages for GUI development, even with the bolted on object systems and language extensions (Qt extends the C++ language).
Using bindings to those frameworks is nice in theory because you don't have to manually manage your own memory or use their type system, but in practice you still need to understand how their types bridge to your language's types and how their memory management bridges with your language's memory management (typically a GC). So while you're dealing with C types and manual memory management less frequently, when you do have to deal with it, it's more complicated than dealing with it in standard C/C++. So (3) is hardly better than (2).
Electron is probably the most cost-effective option, but it has its own problems (notably the high resource consumption that comes from bundling a whole web browser).
With those considerations in mind, learning a new high level language is the least of all problems, especially if the GUI framework is high-quality.